30 Years of the Digest ... founded August 21, 1981
The Telecom Digest for November 2, 2011
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Date: Tue, 01 Nov 2011 05:35:46 -0500 From: email@example.com (Rob Warnock) To: firstname.lastname@example.org. Subject: Re: Edison's powrer network (Was Re: Telegraph turns 150 Message-ID: <IJGdnQ0BS_AfVjLTnZ2dnUVZ_r6dnZ2d@megapath.net> HAncock4 <email@example.com> wrote: +--------------- | In the early part of the 1900s, 25 Hz AC was common. Apparently in | those years it was a good frequency to use on electric motors of that | era (perhaps someone could explain the technical reasons for that.) | In the 1910s-1930s, several railroads electrified with that frequency | and it's still used to this day on certain Amtrak, SEPTA, and NJT lines. +--------------- This Wikipedia article claims that it was due to Niagara Falls: http://en.wikipedia.org/wiki/Utility_frequency#25_Hz_origins ... 25 Hz origins The first generators at the Niagara Falls project, built by Westinghouse in 1895, were 25 Hz because the turbine speed had already been set before alternating current power transmission had been definitively selected. Westinghouse would have selected a low frequency of 30 Hz to drive motor loads, but the turbines for the project had already been specified at 250 RPM. ... Because the Niagara project was so influential on electric power systems design, 25 Hz prevailed as the North American standard for low-frequency AC. And I was going to discuss the use of 400 Hz power in aircraft, but the same article covers that too: ;-} http://en.wikipedia.org/wiki/Utility_frequency#400_Hz ... 400 Hz Frequencies as high as 400 Hz are used in aircraft, spacecraft, submarines, server rooms for computer power, military equipment, and hand-held machine tools. Such high frequencies cannot be economically transmitted long distances, so 400 Hz power systems are usually confined to a building or vehicle. Transformers and motors for 400 Hz are much smaller and lighter than at 50 or 60 Hz, which is an advantage in aircraft and ships. A United States military standard MIL-STD-704 exists for aircraft use of 400 Hz power. A lot of the "whine" you hear in the background of the seat-mounted headset audio (or sometimes even in the overhead cabin announcements) is 400 Hz that has leaked into the audio path. [400 Hz is just slightly higher than G above middle C, so it is quite audible even at low levels.] -Rob +--------------------------------------------------------------+ Rob Warnock <firstname.lastname@example.org> 627 26th Avenue http://rpw3.org/ San Mateo, CA 94403
Date: Tue, 01 Nov 2011 10:23:36 -0500 From: Jim Haynes <email@example.com> To: firstname.lastname@example.org. Subject: Re: Edison's powrer network (Was Re: Telegraph turns 150 Message-ID: <qsWdnZfQD51lky3TnZ2dnUVZ_uKdnZ2d@earthlink.com> On 2011-11-01, Rob Warnock <email@example.com> wrote: > And I was going to discuss the use of 400 Hz power in aircraft, but the > same article covers that too: ;-} > > > http://en.wikipedia.org/wiki/Utility_frequency#400_Hz > > ... > 400 Hz > Frequencies as high as 400 Hz are used in aircraft, spacecraft, > submarines, server rooms for computer power, military equipment, > and hand-held machine tools. Such high frequencies cannot be 400 Hz was popular for some mainframe computers. Maybe the thinking was that they ought to have a motor-generator set anyway for isolation from the power line, so might as well make the generator side 400 Hz while they were at it. Burroughs 220 (vacuum tubes), IBM 7030 (Stretch) (Transistors), and IIRC IBM 709x (transistors) among others. The reasons were the usual, smaller transformers and easier to filter out the ripple. The ripple frequency was 2400 Hz, since they used three phase power.
Date: Tue, 1 Nov 2011 21:34:08 +0000 (UTC) From: firstname.lastname@example.org (Michael Moroney) To: email@example.com. Subject: Re: DC vs. AC grids in NYC, was: Edison's power network (Was Re: Telegraph turns 150 Message-ID: <firstname.lastname@example.org> email@example.com (Garrett Wollman) writes: >In article <firstname.lastname@example.org>, >Michael Moroney <email@example.com> wrote: >>Parts of Buffalo and Niagara Falls NY had 25 Hz power for a while. The >>area didn't get 60 Hz power until 1930, and 60 Hz power consumption didn't >>exceed 25 Hz consumption until 1952. The power company wouldn't sign up >>any new 25 Hz customers after 1947. >Safe Harbor Dam near Lancaster, Pennsylvania, still generates 25 Hz >for the southern parts of the Amtrak (ex-PRR) northeast corridor >electrification system. Amtrak uses static converters and a few >remaining motor-generator sets to supply the rest of the 25 Hz load. >(North of New York City, the NEC uses standard 60 Hz power, 12 kV to >New Haven and thence 25 kV to Boston. I think there is another 25 Hz hydroelectric plant in Maryland that also feeds the Amtrak & nearby 25 Hz system. The oldest hydroelectric plant still in use in the US is in Mechanicville NY. It still generates power at 40 Hz, but the power is converted on-site to feed the grid at 60 Hz. Power from the plant initially fed the GE plant in Schenectady, and was also used for one of the first attempts at high voltage DC power transmission, in 1932. http://en.wikipedia.org/wiki/Mechanicville_Hydroelectric_Plant GE used 40 Hz elsewhere. I've seen a circa-1900 generator in a mill building in Massachusetts. I forget the power rating but I do remember the label stating it generated power at 40 cps at 550 volts.
Date: Tue, 01 Nov 2011 18:45:43 -0700 From: Thad Floryan <firstname.lastname@example.org> To: email@example.com. Subject: Re: DC vs. AC grids in NYC Message-ID: <4EB0A0C7.firstname.lastname@example.org> On 11/1/2011 2:34 PM, Michael Moroney wrote: > [...] > GE used 40 Hz elsewhere. I've seen a circa-1900 generator in a mill > building in Massachusetts. I forget the power rating but I do remember > the label stating it generated power at 40 cps at 550 volts. Whew, I haven't seen that designation, "CPS", used since the mid-1960s when we changed to using "Hz". I was working at the [then Sylvania, later GTE] Electronic Defense Labs in Mountain View CA at the time and one of the oldtimers stated, closely paraphrased: "If (they) wanted to honor someone and keep CPS, the obvious choice would be Charles Proteus Steinmetz." To understand why that could/would have been a good choice: http://en.wikipedia.org/wiki/Charles_Proteus_Steinmetz vs. http://en.wikipedia.org/wiki/Heinrich_Hertz FWIW, Steinmetz fostered the use of AC power along with Tesla. :-)
Date: Tue, 1 Nov 2011 13:30:51 -0700 From: "Jon Danniken" <jonSPAMMENOTdanniken@yahSPAMhoo.com> To: email@example.com. Subject: Re: 60 hz as a time standard Message-ID: <firstname.lastname@example.org> Garrett Wollman wrote: > Jon Danniken wrote: > >> ISTR reading about a plan at one time to alter the line frequency as >> a method of sending an alert for emergencies, similar to the EBS now >> in place. >> >> Anyone remember anything about this? > > You probably saw an episode of the PBS series "History Detectives". > The plan was not to alter the power line frequency, but to superimpose > an RF signal on the line that would activate an alarm that was plugged > into a household outlet. The device worked, but the plan did not, as > the alert carried no information about what to do when the alarm went > off. I think I came across it in an old mail order catalog that supplied kits to hobbyists, but you're probably right about it being an RF signal instead of the timebase (it's been awhile). I always thought it sounded like a neat idea, since not everyone has a TV or radio turned on, but there is always an outlet to plug something into. Speaking of which, I wonder if it was ever considered to include the internet (which would probably now include smart phones) on the EBS. Jon
Date: Wed, 02 Nov 2011 08:52:47 +1100 From: David Clayton <email@example.com> To: firstname.lastname@example.org. Subject: Telephony on TV Message-ID: <email@example.com> I just finished watching an old TV show on DVD where the telephone network was the prime factor in the show. It was the use of a company "Tie Line" between San Francisco to Hawaii that gave away the killer: (Original) Hawaii Five-O season 3 ep 4 "Time and Memories" (starring a young Martin Sheen). The use of the phrase "Tie Line" caught my notice early in the episode, and it put a smile on my face when it turned out to be central to the whole plot. I wonder if there are many other examples on TV or cinema of reasonably obscure telephone technology being used in such an important manner in a plot line? -- Regards, David. David Clayton Melbourne, Victoria, Australia. Knowledge is a measure of how many answers you have, intelligence is a measure of how many questions you have.
Date: Tue, 1 Nov 2011 20:13:54 -0700 (PDT) From: HAncock4 <firstname.lastname@example.org> To: email@example.com. Subject: Re: Telephony on TV Message-ID: <firstname.lastname@example.org> On Nov 1, 5:52 pm, David Clayton <dcstarbox-use...@yahoo.com.au> wrote: > I just finished watching an old TV show on DVD where the telephone network > was the prime factor in the show. It was the use of a company "Tie Line" > between San Francisco to Hawaii that gave away the killer: Could you elaborate how that happened? I don't think tie-line traffic was billed at that time--the point of a tie-line was to provide free communication between two PBXs and billing equipment cost money in that era. Indeed, one of the goals of Centrex was to provide extension outward toll billing which wasn't available before except manually via the PBX operator. > I wonder if there are many other examples on TV or cinema of reasonably > obscure telephone technology being used in such an important manner in a > plot line? Various interesting telephony issues were used to advance the plot in the excellent 1976 film "Three Days of the Condor". The 1960s film "Pillow Talk" featured two single people fighting over use of a shared party line. While this wasn't a major plot line, in a recent TV show, "2 Broke Girls", the wall phone (a green 554 rotary set) rang and a roommate unknowingly answered it. The other roommate explained never to answer that phone because that was the number bill collectors and the landlord called on. In "The Major and the Minor", Ginger Rogers gets a boy to let her use a school switchboard so she can make a toll call important to the plot. She gets her own call through, but screws up other traffic.
Date: Tue, 1 Nov 2011 20:29:56 -0700 (PDT) From: HAncock4 <email@example.com> To: firstname.lastname@example.org. Subject: Re: 60 hz as a time standard Message-ID: <email@example.com> On Oct 31, 6:45 pm, woll...@bimajority.org (Garrett Wollman) wrote: > You probably saw an episode of the PBS series "History Detectives". > The plan was not to alter the power line frequency, but to superimpose > an RF signal on the line that would activate an alarm that was plugged > into a household outlet. The device worked, but the plan did not, as > the alert carried no information about what to do when the alarm went > off. Back in the 1960s we had civil defense training which included what to do if the air raid sirens went off. Everyone had instruction cards. IIRC, there were two types of signals. Radios made at the time had a little triangle at two parts where we were supposed to tune to get instructions. We were not to use the telephone. Every Wednesday at noon for decades the city would sound the sirens briefly as a test. I have no idea if the sirens still exist or are tested, or when they were discontinued. I suspect that the demise of the Soviet Union and the end of the cold-war inspired the demise of the old civil defense program, as well as an aging system. (This would include the old fallout shelters with their cans of water and crackers. Our building repainted the cans to use as paper recycling drums.) As an aside, the loud siren atop the local volunteer firehouse was replaced some years ago with an electronic siren. I think the firefighters have beepers now. ob telephone: Small town telephone directories would list the firechief's home number as the number to call in case of fire.
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